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Session 44 - Circumstellar Material.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
The HST WFPC2 camera has been used to search for circumstellar material around T Tauri and main sequence stars.
Young stellar objects (protostars and T Tauri stars) are often surrounded by optically thick disks. HH30 is a protostar which has a slightly inclined disk ( 7 degrees) appearing as two reflection nebulae separated by a dark lane. Collimated, bipolar jets extend from very close to the obscured protostar. Proper motions of knots in the jets have been determined from images taken about one year apart. GM Aurigae (K. Stapelfeldt et al, this conference) is surrounded by a moderately inclined ( 20 degrees), flattened disk. DG Tau B is embedded in a thick envelope with twin jets emerging at about 25 degrees to the plane of the sky. HL Tau is completely obscured by nebulosity, with no visible disk. Light from the star is visible as reflection from a compact, C-shaped nebula. The two classical T Tauri stars observed, DG Tau and T Tau, are surrounded by cavities illuminated by starlight. In each case, the star appears offset from the cavity apex, indicating that the star has begun to clear the circumstellar environment. DG Tau also has a wide jet. No material was detected around the naked T Tauri stars SAO 76411A and HDE 283572.
Images of Beta Pic show details in the disk to within 1.5 arcsec of the star (C. Burrows et al, this conference). They reveal a thin, almost perfectly edge-on disk with an exponential vertical profile, density power law changeover at 100 AU, and an asymmetry in the inner disk.
Main sequence stars with IRAS infrared excesses and shell-star absorption, properties shared with Beta Pic, were also observed. No disk was detected around Vega, though it is expected to be nearly face on. Also, no disks were seen around the shell stars HR 2174 and HR 4368. Experiments indicate that if a slightly inclined Beta Pic-type disk was present in any of these objects, it should have been detected.
